Fixed length list support

crates/wasm-compose/src/encoding.rs

@@ -649,6 +649,9 @@ impl<'a> TypeEncoder<'a> {
             ComponentDefinedType::Record(r) => self.record(state, r),
             ComponentDefinedType::Variant(v) => self.variant(state, v),
             ComponentDefinedType::List(ty) => self.list(state, *ty),
+            ComponentDefinedType::FixedSizeList(ty, elements) => {
+                self.fixed_size_list(state, *ty, *elements)
+            }
             ComponentDefinedType::Tuple(t) => self.tuple(state, t),
             ComponentDefinedType::Flags(names) => Self::flags(&mut state.cur.encodable, names),
             ComponentDefinedType::Enum(cases) => Self::enum_type(&mut state.cur.encodable, cases),
@@ -709,6 +712,23 @@ impl<'a> TypeEncoder<'a> {
         index
     }
 
+    fn fixed_size_list(
+        &self,
+        state: &mut TypeState<'a>,
+        ty: ct::ComponentValType,
+        elements: u32,
+    ) -> u32 {
+        let ty = self.component_val_type(state, ty);
+        let index = state.cur.encodable.type_count();
+        state
+            .cur
+            .encodable
+            .ty()
+            .defined_type()
+            .fixed_size_list(ty, elements);
+        index
+    }
+
     fn tuple(&self, state: &mut TypeState<'a>, tuple: &TupleType) -> u32 {
         let types = tuple
             .types
@@ -1228,7 +1248,9 @@ impl DependencyRegistrar<'_, '_> {
             ComponentDefinedType::Primitive(_)
             | ComponentDefinedType::Enum(_)
             | ComponentDefinedType::Flags(_) => {}
-            ComponentDefinedType::List(t) | ComponentDefinedType::Option(t) => self.val_type(*t),
+            ComponentDefinedType::List(t)
+            | ComponentDefinedType::FixedSizeList(t, _)
+            | ComponentDefinedType::Option(t) => self.val_type(*t),
             ComponentDefinedType::Own(r) | ComponentDefinedType::Borrow(r) => {
                 self.ty(ComponentAnyTypeId::Resource(*r))
             }

crates/wasm-encoder/src/component/types.rs

@@ -593,6 +593,13 @@ impl ComponentDefinedTypeEncoder<'_> {
         ty.into().encode(self.0);
     }
 
+    /// Define a fixed size list type.
+    pub fn fixed_size_list(self, ty: impl Into<ComponentValType>, elements: u32) {
+        self.0.push(0x67);
+        ty.into().encode(self.0);
+        elements.encode(self.0);
+    }
+
     /// Define a tuple type.
     pub fn tuple<I, T>(self, types: I)
     where

crates/wasm-encoder/src/reencode/component.rs

@@ -767,6 +767,9 @@ pub mod component_utils {
             wasmparser::ComponentDefinedType::List(t) => {
                 defined.list(reencoder.component_val_type(t));
             }
+            wasmparser::ComponentDefinedType::FixedSizeList(t, elements) => {
+                defined.fixed_size_list(reencoder.component_val_type(t), elements);
+            }
             wasmparser::ComponentDefinedType::Tuple(t) => {
                 defined.tuple(t.iter().map(|t| reencoder.component_val_type(*t)));
             }

crates/wasm-wave/src/value/ty.rs

@@ -10,6 +10,7 @@ pub struct Type(pub(super) TypeEnum);
 pub(super) enum TypeEnum {
     Simple(SimpleType),
     List(Arc<ListType>),
+    FixedSizeList(Arc<ListType>, u32),
     Record(Arc<RecordType>),
     Tuple(Arc<TupleType>),
     Variant(Arc<VariantType>),
@@ -55,6 +56,15 @@ impl Type {
         Self(TypeEnum::List(Arc::new(ListType { element })))
     }
 
+    /// Returns a list type with the given element type.
+    pub fn fixed_size_list(element_type: impl Into<Self>, elements: u32) -> Self {
+        let element = element_type.into();
+        Self(TypeEnum::FixedSizeList(
+            Arc::new(ListType { element }),
+            elements,
+        ))
+    }
+
     /// Returns a record type with the given field types. Returns None if
     /// `fields` is empty.
     pub fn record<T: Into<Box<str>>>(
@@ -189,6 +199,7 @@ impl WasmType for Type {
         match self.0 {
             TypeEnum::Simple(simple) => simple.0,
             TypeEnum::List(_) => WasmTypeKind::List,
+            TypeEnum::FixedSizeList(_, _) => WasmTypeKind::FixedSizeList,
             TypeEnum::Record(_) => WasmTypeKind::Record,
             TypeEnum::Tuple(_) => WasmTypeKind::Tuple,
             TypeEnum::Variant(_) => WasmTypeKind::Variant,

crates/wasm-wave/src/value/wit.rs

@@ -70,6 +70,9 @@ impl<'a> TypeResolver<'a> {
             TypeDefKind::Option(some_type) => self.resolve_option(some_type),
             TypeDefKind::Result(result) => self.resolve_result(result),
             TypeDefKind::List(element_type) => self.resolve_list(element_type),
+            TypeDefKind::FixedSizeList(element_type, elements) => {
+                self.resolve_fixed_size_list(element_type, *elements)
+            }
             TypeDefKind::Type(Type::Bool) => Ok(value::Type::BOOL),
             TypeDefKind::Type(Type::U8) => Ok(value::Type::U8),
             TypeDefKind::Type(Type::U16) => Ok(value::Type::U16),
@@ -145,6 +148,11 @@ impl<'a> TypeResolver<'a> {
         let element_type = self.resolve_type(*element_type)?;
         Ok(value::Type::list(element_type))
     }
+
+    fn resolve_fixed_size_list(&self, element_type: &Type, elements: u32) -> ValueResult {
+        let element_type = self.resolve_type(*element_type)?;
+        Ok(value::Type::fixed_size_list(element_type, elements))
+    }
 }
 
 #[cfg(test)]

crates/wasm-wave/src/wasm/ty.rs

@@ -20,6 +20,7 @@ pub enum WasmTypeKind {
     Char,
     String,
     List,
+    FixedSizeList,
     Record,
     Tuple,
     Variant,
@@ -48,6 +49,7 @@ impl std::fmt::Display for WasmTypeKind {
             WasmTypeKind::Char => "char",
             WasmTypeKind::String => "string",
             WasmTypeKind::List => "list",
+            WasmTypeKind::FixedSizeList => "list<_,N>",
             WasmTypeKind::Record => "record",
             WasmTypeKind::Tuple => "tuple",
             WasmTypeKind::Variant => "variant",

crates/wasm-wave/src/writer.rs

@@ -75,6 +75,16 @@ impl<W: Write> Writer<W> {
                 }
                 self.write_str("]")
             }
+            WasmTypeKind::FixedSizeList => {
+                self.write_str("[")?;
+                for (idx, val) in val.unwrap_list().enumerate() {
+                    if idx != 0 {
+                        self.write_str(", ")?;
+                    }
+                    self.write_value(&*val)?;
+                }
+                self.write_str("]")
+            }
             WasmTypeKind::Record => {
                 self.write_str("{")?;
                 let mut first = true;

crates/wasmparser/src/features.rs

@@ -254,6 +254,11 @@ define_wasm_features! {
         /// Corresponds to the 📝 character in
         /// <https://github.com/WebAssembly/component-model/blob/main/design/mvp/Explainer.md>.
         pub cm_error_context: CM_ERROR_CONTEXT(1 << 30) = false;
+        /// Support for fixed size lists
+        ///
+        /// Corresponds to the 🔧 character in
+        /// <https://github.com/WebAssembly/component-model/blob/main/design/mvp/Explainer.md>.
+        pub cm_fixed_size_list: CM_FIXED_SIZE_LIST(1 << 31) = false;
     }
 }
 

crates/wasmparser/src/readers/component/types.rs

@@ -441,6 +441,8 @@ pub enum ComponentDefinedType<'a> {
     Variant(Box<[VariantCase<'a>]>),
     /// The type is a list of the given value type.
     List(ComponentValType),
+    /// The type is a fixed size list of the given value type.
+    FixedSizeList(ComponentValType, u32),
     /// The type is a tuple of the given value types.
     Tuple(Box<[ComponentValType]>),
     /// The type is flags with the given names.
@@ -503,8 +505,9 @@ impl<'a> ComponentDefinedType<'a> {
             },
             0x69 => ComponentDefinedType::Own(reader.read()?),
             0x68 => ComponentDefinedType::Borrow(reader.read()?),
-            0x65 => ComponentDefinedType::Future(reader.read()?),
+            0x67 => ComponentDefinedType::FixedSizeList(reader.read()?, reader.read_var_u32()?),
             0x66 => ComponentDefinedType::Stream(reader.read()?),
+            0x65 => ComponentDefinedType::Future(reader.read()?),
             x => return reader.invalid_leading_byte(x, "component defined type"),
         })
     }

crates/wasmparser/src/validator/component.rs

@@ -724,9 +724,9 @@ impl ComponentState {
                         .map(|t| types.type_named_valtype(t, set))
                         .unwrap_or(true)
             }
-            ComponentDefinedType::List(ty) | ComponentDefinedType::Option(ty) => {
-                types.type_named_valtype(ty, set)
-            }
+            ComponentDefinedType::List(ty)
+            | ComponentDefinedType::FixedSizeList(ty, _)
+            | ComponentDefinedType::Option(ty) => types.type_named_valtype(ty, set),
 
             // The resource referred to by own/borrow must be named.
             ComponentDefinedType::Own(id) | ComponentDefinedType::Borrow(id) => {
@@ -3475,6 +3475,18 @@ impl ComponentState {
             crate::ComponentDefinedType::List(ty) => Ok(ComponentDefinedType::List(
                 self.create_component_val_type(ty, offset)?,
             )),
+            crate::ComponentDefinedType::FixedSizeList(ty, elements) => {
+                if !self.features.cm_fixed_size_list() {
+                    bail!(
+                        offset,
+                        "Fixed size lists require the component model fixed size list feature"
+                    )
+                }
+                Ok(ComponentDefinedType::FixedSizeList(
+                    self.create_component_val_type(ty, offset)?,
+                    elements,
+                ))
+            }
             crate::ComponentDefinedType::Tuple(tys) => {
                 self.create_tuple_type(tys.as_ref(), types, offset)
             }

crates/wasmparser/src/validator/component_types.rs

@@ -1084,6 +1084,8 @@ pub enum ComponentDefinedType {
     Variant(VariantType),
     /// The type is a list.
     List(ComponentValType),
+    /// The type is a fixed size list.
+    FixedSizeList(ComponentValType, u32),
     /// The type is a tuple.
     Tuple(TupleType),
     /// The type is a set of flags.
@@ -1124,7 +1126,7 @@ impl TypeData for ComponentDefinedType {
             Self::Record(r) => r.info,
             Self::Variant(v) => v.info,
             Self::Tuple(t) => t.info,
-            Self::List(ty) | Self::Option(ty) => ty.info(types),
+            Self::List(ty) | Self::FixedSizeList(ty, _) | Self::Option(ty) => ty.info(types),
             Self::Result { ok, err } => {
                 let default = TypeInfo::new();
                 let mut info = ok.map(|ty| ty.type_info(types)).unwrap_or(default);
@@ -1153,7 +1155,7 @@ impl ComponentDefinedType {
             | Self::Borrow(_)
             | Self::Future(_)
             | Self::Stream(_) => false,
-            Self::Option(ty) => ty.contains_ptr(types),
+            Self::Option(ty) | Self::FixedSizeList(ty, _) => ty.contains_ptr(types),
             Self::Result { ok, err } => {
                 ok.map(|ty| ty.contains_ptr(types)).unwrap_or(false)
                     || err.map(|ty| ty.contains_ptr(types)).unwrap_or(false)
@@ -1174,6 +1176,9 @@ impl ComponentDefinedType {
                 lowered_types,
             ),
             Self::List(_) => lowered_types.push(ValType::I32) && lowered_types.push(ValType::I32),
+            Self::FixedSizeList(ty, length) => {
+                (0..(*length).min(8192)).all(|_n| ty.push_wasm_types(types, lowered_types))
+            }
             Self::Tuple(t) => t
                 .types
                 .iter()
@@ -1248,6 +1253,7 @@ impl ComponentDefinedType {
             ComponentDefinedType::Flags(_) => "flags",
             ComponentDefinedType::Option(_) => "option",
             ComponentDefinedType::List(_) => "list",
+            ComponentDefinedType::FixedSizeList(_, _) => "fixed size list",
             ComponentDefinedType::Result { .. } => "result",
             ComponentDefinedType::Own(_) => "own",
             ComponentDefinedType::Borrow(_) => "borrow",
@@ -1985,7 +1991,9 @@ impl TypeAlloc {
                     }
                 }
             }
-            ComponentDefinedType::List(ty) | ComponentDefinedType::Option(ty) => {
+            ComponentDefinedType::List(ty)
+            | ComponentDefinedType::FixedSizeList(ty, _)
+            | ComponentDefinedType::Option(ty) => {
                 self.free_variables_valtype(ty, set);
             }
             ComponentDefinedType::Result { ok, err } => {
@@ -2127,9 +2135,9 @@ impl TypeAlloc {
                         .map(|t| self.type_named_valtype(t, set))
                         .unwrap_or(true)
             }
-            ComponentDefinedType::List(ty) | ComponentDefinedType::Option(ty) => {
-                self.type_named_valtype(ty, set)
-            }
+            ComponentDefinedType::List(ty)
+            | ComponentDefinedType::FixedSizeList(ty, _)
+            | ComponentDefinedType::Option(ty) => self.type_named_valtype(ty, set),
 
             // own/borrow themselves don't have to be named, but the resource
             // they refer to must be named.
@@ -2314,7 +2322,9 @@ where
                     }
                 }
             }
-            ComponentDefinedType::List(ty) | ComponentDefinedType::Option(ty) => {
+            ComponentDefinedType::List(ty)
+            | ComponentDefinedType::FixedSizeList(ty, _)
+            | ComponentDefinedType::Option(ty) => {
                 any_changed |= self.remap_valtype(ty, map);
             }
             ComponentDefinedType::Result { ok, err } => {
@@ -3203,6 +3213,14 @@ impl<'a> SubtypeCx<'a> {
             (Variant(_), b) => bail!(offset, "expected {}, found variant", b.desc()),
             (List(a), List(b)) | (Option(a), Option(b)) => self.component_val_type(a, b, offset),
             (List(_), b) => bail!(offset, "expected {}, found list", b.desc()),
+            (FixedSizeList(a, asize), FixedSizeList(b, bsize)) => {
+                if asize != bsize {
+                    bail!(offset, "expected fixed size {bsize}, found size {asize}")
+                } else {
+                    self.component_val_type(a, b, offset)
+                }
+            }
+            (FixedSizeList(_, _), b) => bail!(offset, "expected {}, found list", b.desc()),
             (Option(_), b) => bail!(offset, "expected {}, found option", b.desc()),
             (Tuple(a), Tuple(b)) => {
                 if a.types.len() != b.types.len() {

crates/wasmprinter/src/component.rs

@@ -169,6 +169,19 @@ impl Printer<'_, '_> {
         Ok(())
     }
 
+    pub(crate) fn print_fixed_size_list_type(
+        &mut self,
+        state: &State,
+        element_ty: &ComponentValType,
+        elements: u32,
+    ) -> Result<()> {
+        self.start_group("list ")?;
+        self.print_component_val_type(state, element_ty)?;
+        self.result.write_str(&format!(" {elements}"))?;
+        self.end_group()?;
+        Ok(())
+    }
+
     pub(crate) fn print_tuple_type(
         &mut self,
         state: &State,
@@ -265,6 +278,9 @@ impl Printer<'_, '_> {
             ComponentDefinedType::Record(fields) => self.print_record_type(state, fields)?,
             ComponentDefinedType::Variant(cases) => self.print_variant_type(state, cases)?,
             ComponentDefinedType::List(ty) => self.print_list_type(state, ty)?,
+            ComponentDefinedType::FixedSizeList(ty, elements) => {
+                self.print_fixed_size_list_type(state, ty, *elements)?
+            }
             ComponentDefinedType::Tuple(tys) => self.print_tuple_type(state, tys)?,
             ComponentDefinedType::Flags(names) => self.print_flag_or_enum_type("flags", names)?,
             ComponentDefinedType::Enum(cases) => self.print_flag_or_enum_type("enum", cases)?,

crates/wast/src/component/binary.rs

@@ -107,7 +107,11 @@ fn encode_defined_type(encoder: ComponentDefinedTypeEncoder, ty: &ComponentDefin
             }));
         }
         ComponentDefinedType::List(l) => {
-            encoder.list(l.element.as_ref());
+            if let Some(elements) = l.elements {
+                encoder.fixed_size_list(l.element.as_ref(), elements);
+            } else {
+                encoder.list(l.element.as_ref());
+            }
         }
         ComponentDefinedType::Tuple(t) => {
             encoder.tuple(t.fields.iter());

crates/wast/src/component/types.rs

@@ -584,13 +584,18 @@ impl<'a> Parse<'a> for Refinement<'a> {
 pub struct List<'a> {
     /// The element type of the array.
     pub element: Box<ComponentValType<'a>>,
+    /// Optional fixed size
+    pub elements: Option<u32>,
 }
 
 impl<'a> Parse<'a> for List<'a> {
     fn parse(parser: Parser<'a>) -> Result<Self> {
         parser.parse::<kw::list>()?;
+        let tp = parser.parse()?;
+        let elements = parser.parse()?;
         Ok(Self {
-            element: Box::new(parser.parse()?),
+            element: Box::new(tp),
+            elements,
         })
     }
 }

crates/wit-component/src/encoding.rs

@@ -320,6 +320,7 @@ impl TypeContents {
                 }
                 TypeDefKind::Enum(_) => Self::empty(),
                 TypeDefKind::List(t) => Self::for_type(resolve, t) | Self::LIST,
+                TypeDefKind::FixedSizeList(t, _elements) => Self::for_type(resolve, t),
                 TypeDefKind::Type(t) => Self::for_type(resolve, t),
                 TypeDefKind::Future(_) => Self::empty(),
                 TypeDefKind::Stream(_) => Self::empty(),

crates/wit-component/src/encoding/types.rs

@@ -144,6 +144,12 @@ pub trait ValtypeEncoder<'a> {
                         encoder.list(ty);
                         ComponentValType::Type(index)
                     }
+                    TypeDefKind::FixedSizeList(ty, elements) => {
+                        let ty = self.encode_valtype(resolve, ty)?;
+                        let (index, encoder) = self.defined_type();
+                        encoder.fixed_size_list(ty, *elements);
+                        ComponentValType::Type(index)
+                    }
                     TypeDefKind::Type(ty) => self.encode_valtype(resolve, ty)?,
                     TypeDefKind::Future(ty) => self.encode_future(resolve, ty)?,
                     TypeDefKind::Stream(ty) => self.encode_stream(resolve, ty)?,